A known variable valve timing control device includes a driven side rotation member provided coaxially to a driving side rotation member, a fluid pressure chamber defined between the driving side rotation member and the driven side rotation member, and an intermediate lock mechanism for selectively switching a locked state where a relative rotational phase of the driven side rotation member to the driving side rotation member is restrained at an intermediate lock phase positioned between a most advanced angle phase and a most retarded angle phase, and an unlocked state where the restraint is released (e.g., see JP2012-193731A (hereinafter referred to as Patent reference 1) and JP2010-223172A (hereinafter referred to as Patent reference 2).
The variable valve timing control device disclosed in Patent reference 1 includes a first electromagnetic valve (corresponding to a spool, an actuator, and a spring in the reference) for controlling the supplying and draining of the operation fluid to and from the fluid pressure chamber and a second electromagnetic valve (corresponding to a spool, an actuator, and a spring in the reference) for controlling the supplying and draining of the operation fluid from and to the intermediate lock mechanism separately from the first electromagnetic valve. The first electromagnetic valve and the second electromagnetic valve are provided coaxially to the driving side rotation member and the driven side rotation member. The variable valve timing control device disclosed in Patent reference 2 includes a first electromagnetic valve (corresponding to a first switching valve in the reference) for controlling the supplying and draining of the operation fluid to and from the fluid pressure chamber, a second electromagnetic valve (corresponding to a second switching valve in the reference) for controlling the supplying and draining of the operation fluid from and to the intermediate lock mechanism separately from the first electromagnetic valve, and a single pump supplying the operation fluid to the first electromagnetic valve and the second electromagnetic valve. The first electromagnetic valve and the second electromagnetic valve are provided on an axis which is different from an axis of the driving side rotation member and the driven side rotation member and is positioned closer to a camshaft compared to the position of the driving side rotation member and the driven side rotation member relative to the camshaft.
According to the variable valve timing control device disclosed in Patent reference 1 and Patent reference 2, because the switching control for locking and unlocking the intermediate lock mechanism is performed independently from the supplying and draining control of the operation fluid to and from the fluid pressure chamber, the precision for setting the relative rotation phase is assumed to be high.
Notwithstanding, according to the construction disclosed in Patent reference 1, because the first electromagnetic valve and the second electromagnetic valve are provided coaxially to the driving side rotation member and the driven side rotation member, an axial length of the variable valve timing control device is increased. Further, according to the construction disclosed in Patent reference 2, space for mounting the first electromagnetic valve and the second electromagnetic valve and numbers of fluid passages for supplying and draining the operation fluid are required to be provided at a side closer to the camshaft relative to the driving side rotation member and the driven side rotation member. Thus, according to the known variable valve timing control devices, the degree of freedom for the positioning of parts is low because of the positional relations with respect to surrounding components that are placed close to each other.
Because the temperature of the operation fluid is low when starting the engine, adequate fluid volume necessary for unlocking the intermediate lock mechanism and changing the relative rotational phase cannot be ensured. Particularly, according to the construction for supplying the operation fluid to the first electromagnetic valve and the second electromagnetic valve simultaneously as a pump disclosed in Patent reference 2, time is required for unlocking the intermediate lock mechanism and supplying adequate volume of the fluid to the fluid pressure chamber when starting the engine.
A need thus exists for a variable valve timing control device which is not susceptible to the drawback mentioned above.